Electrode structure



Alig. 25, 1931. F. s. MCCULLOUGH 20,

ELECTRODE STRUCTURE Filed Jan. 5, 1926 Eva/2 7 4 Patented Aug. 25,1931

UNITED STATES PATENT OFFICE FREDERICK S. McCULLOUGI-I, OF EDGEWOOD, PENNSYLVANIA, ASSIGNOR TO STUPAKOFF LABORATORIES, INC., OF PITTSBURGH, PENNSYLVANIA, A CORPORATION ELECTRODE STRUCTURE Application filed January 5, 1926. Serial No. 79,350.

This invention relates to electrode structures, and particularly to an electrode structure for use in thermionic devices having a heated electrode. I

Certain types of electrode devices have been proposed wherein a cathode is pro vided which is in the nature of a metal body having a porcelain filling, the porcelain filling having an. imbedded heating wire therein. operation of such devices that due to the high thermal resistance of the porcelain, the heating wire must be operated at an excessively high temperature in order to maintain the, cathode at a temperature sufficient to sustain thermionic emission. This is detrimental to the life of the heating wire. It has also been found that where the heating wire is maintained at such a temperature, that a chemical reaction occurs between the refractory substance and the heating wire, which is also injurious to the heating wire and shortens the life of the electrode.

Such a construction, however, has certain advantages in that it enables a heating wire to be supported within an electrode structure in such a way as to be insulated from the electrode structure, and permits of the use of a single supporting stem for rigidly mounting the entireelectrode structure within an enclosing vessel.

Another advantage of this structure is that it provides a support for the heating wire of a rather rigid nature so that the heating wire is not so apt to be injured by vibration, and an electrode device having .an electrode of this structure, particularly a radio tube, does not have the microphonic qualities found in radio tubes having the usual form of electrode.

According to the present invention,'it is proposed to provide an electrode structure wherein the advantages inherent in the structure heretofore provided are obtained, but wherein the disadvantages arising from the use of a mass of porcelain in the electrode are effectively eliminated. It may also be noted that where a mass of porcelain, or other refractory material, is con- It has been found in the taincd within an electrode structure to be mounted in an evacuated vessel that such a mass of porcelain is difficult to degasify to that degree of satisfaction necessary in devices of this kind. According to the present invention, this mass of porcelain is eliminated, thereby rendering the successful degasification of the tube more certain.

The invention may be readily understood by reference to the accompanying drawings, which illustrate a preferred form of my invention, but to the exact construction of.

which the invention is not confined.

In the drawings:

Figure 1 represents an enlarged vertical section through an electrode structure embodying the present invention;

Figure 2 represents a section of line IIII of Figure 1;

Figure 3 is an elevation of a cathode member embodying my invention, showing a in the plane modified arrangement for the heating wire.

Inthe drawings, 2 designates a supporting member, which could be of any suitable nature, such as the stem of an evacuated vessel of any wellknown type, or any other suitable supporting element. Carried by the supporting base 2 is a stem 3, on which is carried an electrode 4. This electrode 4 is preferably in the form of a cylinder which may, if desired, be of a magnetic material such as nickel, and which preferably has a coating on the surface thereof adapted to produce a relatively high electron emission at relatively low temperatures. Passing through the cylinder is a heating wire 5 which is preferably looped in a hairpin formation, but need not be so looped or need not be of such formation. The heating wire 5 is maintained in' spaced relation to the electrode 4 and is rigidly supported in the electrode 4, and the looped portions of the wire are maintained in proper spaced relation by means of a plurality, of suitable beads or spacers 6 of an insulating material. These beads are relatively small as compared with the total length of the heating wire and electrode so that their mass is notfconsiderable.

The beads 6 are placed at an appreciable v distance apart whereby the main extent of the heating wire is exposed. The portion of the heating wire which is embedded in the porcelain heads is of such small extent that overheating is not likely to occur. Consequently, injury to the heating wire by reason of overheating or by reason of chemical reaction with the refractory material at excessively high temperatures is avoided. At the same time, the heating wire has suflicient support so that it is fairly rigid, making the electrode structure sturdy and durable and not likely to be injured by the handling to which devices of this kind are ordinarily subject. The heating wire furthermore has sufficient rigidity of support so as not to introduce mierophonic disturbances into the tube.

If the electrode is used in a radio tube and the shell 4: is of a magnetic material, and is grounded, as indicated in Figure 1 of the drawings, it will effectively reduce or eliminate distortion or ripple in the output circuit of the tube resulting from variations or pulsations in the heater wire circuit.

The coating on the shell 4 is of a more or less refractory nature, such as an alkaline earth substance or a rare earth oxide, and in addition to increasing the electron emissitivity, effects an even distribution of heat over the surface of the member 4.

In Figure 3, I have shown this coating on the exterior of the cathodennember 7. I have shown the member 7 as being heated by a single wire 8 passing continuously therethrough. Beads 9 serve to space the member 7 from the wire 8.

While I have shown and described a preferred embodiment of my invention, it will be obvious that various changes in the construction and location of the various parts may be changed within the spirit of my invention and under the scope of the appended claims.

I claim as my invention:

1. A cathode structure comprising a cylindrical metal shell open at least one end having a plurality of spaced apart refractory discs therein in contact with the inner walls thereof and a heater wire in the form of a reentrant loop within the shell supported by the refractory discs out of contact with the metal shell, the terminals of the loop projecting from the open end of the cylinder.

2. A cathode structure comprising a cylindrical metal shell having a plurality of spaced apart refractory discs therein in contact with the inner walls thereof, said discs being disposed at the ends thereof and intermediate the ends, and a heater wire passing through the refractory discs and supported thereby out of contact with the shell.

3. A cathode structure comprising a tubular metal member, a reentrant looped heater wire within the member, and refractory spacing elements at intervals along the length of the metal member supporting the heater-wire at a plurality of points and holding said heater wire out of contact with the metal shell and maintaining the two strands of said loop out of contact with each other, the greater portion of the heater wire being directly exposed to the interior of the metal member.

4. A cathode structure comprising a tubular metal member having spaced apart refractory elements on the interior thereof at intervals along its length contacting with the inside of the tubular metal member, and a looped heater wire having substantially parallel strands coaxially disposed within the tubular metal member and having the parallel strands supported adjacent the ends thereof and at least one point intermediate its ends by said refractory elements which maintain the strands out of contact with each other and in spaced relation to the metal member.

5. An indirectly heated cathode comprising a metal sleeve constitutin the body of the cathode, a looped heater wire within the sleeve having its two ends at the same end of the cylinder, said wire being exposed to the interior of the metal sleeve throughout the greater portion of its length, a plug of refractory material adjacent one end of the sleeve through which the looped heater wire passes serving to keep the wire in spaced relation to the interior of the sleeve, and a second plug of insulating material at the other end of the sleeve also serving to support the heater wire out of contact with the interior of the sleeve.

6. An indirectly heated cathode comprising a metal sleeve, a reentrant looped heater Wire within the sleeve, and insulator elements within the sleeve disposed along the looped heater wire serving to maintain the strands of the loop out of contact with each other and supporting the heater wire. out of contact with the interior of the sleeve, the wire being exposed to the interior of the sleeve along themajor portion of its entire length.

7. A cathode construction con'iprising a sleeve member, a heater wire within the sleeve member, and insulating means Within the sleeve member for supporting the wire, said insulating means having portions enclosing the wire at spaced internals so as to provide alternate stretches of exposed wire between portions of the wire enclosed by the insulating means. said insulating means embracing the wire intermediate. the ends of the sleeve and adjacent the ends of the sleeve.

8. A cathode construction comprising a sleeve, a reentrant looped heater wire within the sleeve having the major portion of its length exposed to the interior of the sleeve, and insulating means within the sleeve di-' rectly contacting with the heater wire and said sleeve and supporting the same out bf Contact with the sleeve. 2

In testimony whereof I have hereunto set my hand.

FREDERICK s. MoCULLOUGHQ 

